# 只声明了变量名，指定具体的值 None
money = None
# <class 'NoneType'> None
print(type(money), money)

money = 90
print(type(money), money)


def check_age(age):
    if age > 18:
        # 不声明返回值，则默认返回 None
        print("Sucess")
    else:
        return None


age = check_age(19)

if not age:
    print("未满18岁")
else:
    print("已满18岁")
